In the prior art, a sugar cane crushing mill comprises a two roll mill module consisting of a top roll and a feed roll or a three roll mill module consisting of a top roll, a feed roll and a discharge roll. These rolls are made of cast iron or cast steel and are provided with peripheral grooves. A plurality of these main crushing mill modules are provided in tandem forming the cane crushing mill.
The main drawbacks of these cane crushing mills are:
1. The bulk density of the prepared cane/bagasse being fed to the mills is very low. This results into a very low cane crushing rate of the mill. PA1 2. There is a slippage between the cane/bagasse and rolls resulting in higher frictional losses and thus, besides low cane crushing rate, power consumption is more. PA1 3. Feed to discharge operating opening ratio is higher due to low bulk density and slippage of cane/bagasse. This causes lower juice extraction and higher juice reabsorption. As used herein, feed to discharge operating opening ratio means the ratio of the gap between top roll and feed roll to the gap between top roll and discharge roll in operating position of the mill, i.e. in lifted/shifted position of the rolls against the hydraulic pressure.
In the prior art, to increase the bulk density of the cane/bagasse, feeding equipment in the form of over/under feeder rollers provided above or below the prepared cane mat, being fed through a conveyer and/or Donnelly chute, are incorporated with the crushing mill module. The over or under feeder roller has peripheral grooves or axial or helical ribs.
This feeding equipment is not able to provide any significant relief to the drawbacks of the prior art cane crushing mill, described hereinbefore, due to its inherent limitations of developing pressure.
Further, in the prior art, a pair of grooved feeder rollers or a pair of toothed feeder rollers are incorporated in front of the feed and top rolls of the main crushing mill module, nearly in a parallel plane and in-line, i.e. having approximately the same central axis. A closed stationary diverging pressure chute, having a wider opening towards the main mill rolls, is required to be connected between the pair of feeder rollers and the main crushing mill rolls.
The main drawback of this arrangement is that the speed of the cane in comparison with the mill rolls surface speed is very low. This results in more frictional losses, more wear and tear and choking in the cane feeding system. As a result of this undue pressure leads to damage of various parts and hence there is frequent breakdown of the mill, resulting into low milling capacity, high power consumption and maintenance cost. Additionally, skilled personnel are required for maintenance and operation of these mills.
Furthermore, in the prior art sugar cane crushing mills, the cush-cush soaked with juice in the strainer is fed into the mill module, under the strainer, for milling along with the bagasse. The main drawback of this system is that the high purity of the juice in the cush-cush is recirculated through the mill module. This creates extra slippage, juice overloading and poor juice drainage and results in lower capacity and efficiency of milling.